In recent years, in the production of semiconductor device and liquid crystal display device, advances in lithography techniques have led to rapid progress in the miniaturization of semiconductor device and liquid crystal display device. Typically, these techniques for achieving further miniaturization involve shortening of the wavelength of the exposure light source. Until recently, ultraviolet radiation such as g-lines and i-lines have been used as the exposure light source, but recently, mass production using KrF excimer lasers (248 nm) has been employed, and even ArF excimer lasers (193 nm) are now starting to be introduced. In addition, lithography techniques using F2 excimer lasers (157 nm), EUV (extreme ultraviolet radiation), or EB (electron beams) as a light source (radiation source) are also being investigated.
There has been required a resist used in such a light source having a short wavelength that satisfies a high resolution capable of reproducing a pattern with a very minute dimension and high sensitivity for the light source having a short wavelength.
One example of a known resist is a chemically amplified resist containing a base resin and an acid generator (hereinafter, referred to as PAG) that generates acid on exposure. As the chemically amplified resist, a positive type resist that increases alkali solubility of an exposed portion and a negative type resist that decreases alkali solubility of an exposed portion can be mentioned.
So far, as the base resin of the chemically amplified resist, polyhydroxystyrene (PHS), which exhibits high transparency to KrF excimer laser, or PHS resins of which the hydroxyl groups have been protected with an acid dissociable dissolution inhibiting group have been used. However, since the PHS resins include an aromatic ring such as a benzene ring, transparency to light having a short wavelength of shorter than 248 nm, that is, 193 nm is not sufficient. Hence, there is a problem in that the chemically amplified resist using PHS resins as base resin components exhibits low resolution in a process of using light of 193 nm.
Therefore, as the base resins of the resist which has been currently used in ArF excimer laser lithography, resins (acrylic resins) having a structural unit derived from (meth)acrylate ester in a main chain have been generally used because of their excellent transparency to light of around 193 nm (see, Patent Document 1).
Furthermore, the resists are required to exhibit a variety of excellent lithographic properties such as the depth of focus (DOF) and resist pattern shape, in addition to sensitivity and resolution.
[Patent Literature 1] Japanese Unexamined Patent Publication 2003-167347